A standard Type 51 oil-filter assembly sold by Maschinenfabrik Reinhausen as BA 18/03de-1196/1000 has a normally stationary base unit formed as an upwardly open cylindrical can on which or in which is mounted a pump-motor unit. A cover closes the top of the can and normally has a fitting connected via a flexible oil line to the piece of equipment whose oil is being filtered. The oil is filtered by being passed through a sleeve-like filter insert held in the can. A simple paper filter is used to eliminate particles from the oil and composite filters are used in high-humidity environments to also strip out any water droplets.
The cover for the assembly has a rod that projects axially through the filter insert which is secured to it by a nut and washer. As a result changing the filter insert is a very messy job. The cover and attached insert must normally be completely disconnected so that a tool can be applied to the nut to loosen it and allow the old insert to be removed. Since the filter insert itself is soaked in oil, such a job is sure to spread oil around the work space. In addition the mass of the cover and filled insert are considerable so that it is not easily lifted out of the base unit. At the very least the area around the filter assembly can be counted on to be well sprinkled with dirty oil during such a filter change.